Construction machines are frequently used by its nature in a place whose road surface is in a bad condition as compared with general vehicles. Some types of construction machines employ four-wheel drive or six-wheel drive. However, on a soft ground such as a mine or a construction site, since positional differences between the wheels lead to different friction coefficients between the wheels and the road surface, even the above types of construction machines suffer from the slip of part of the driving wheels, so that a driving torque cannot be transmitted to the other driving wheels. In such a case, most of engine output is used to drive the slipping driving wheel or wheels, so that a sufficient amount of the driving force cannot be transmitted to the road surface, thereby reducing acceleration.
As devices for controlling the driving force to the wheels of the above types of construction machines, there has been known a traction control (hereinafter referred to as TCS) device capable of adjusting a brake torque to each wheel and a differential-lock control device capable of locking a differential in a differential mechanism between right and left driving wheels or between front and rear wheels (see, for instance, Patent Literature 1).
Patent Literature 1 teaches a construction machine including an inter-axle differential as a differential device capable of distributing engine output to the front, center and rear wheels, in which a sign of slip of the front wheels are detected based on the rotation speed of a transmission output shaft, the rotation speed of a front output shaft of the inter-axle differential, and the rotation speed of a rear output shaft of the inter-axle differential. When the sign is detected, a differential-lock amount of the inter-axle differential is controlled.